1. Field of the Invention
The invention relates to a magnetic sensor capable of detecting a change in a magnetic field with high sensitivity.
2. Description of the Related Art
Generally, to accurately detect a weak control current flowing through a circuit in a control apparatus, a method of connecting resisters in series in the circuit and measuring a voltage drop of the resisters is used. However, in this case, a load different from that of a control system is applied and any adverse affect may occur to the control system. Accordingly, a method of indirectly measuring a control current by detecting the gradient of the induction magnetic field generated by the control current has been used. In particular, a magnetic sensor in which giant magneto-resistive elements (hereinafter, GMR element) expressing giant magneto-resistive effect are arranged in the induction magnetic field by the control current to detect the gradient has been proposed (for example, see U.S. Pat. No. 5,621,377).
In a related matter, a technique that uses a magnetic sensor having GMR elements to perform flaw detection on a surface of a metallic substrate and the like has been proposed. Furthermore, as an angle sensor that measures a direction of the geomagnetism or a rotational angle of rotating magnetic flux on a certain plane, some magnetic sensor using GMR elements has been developed (see Japanese Patent Application Laid-open Nos. 2000-35470 and 2002-303536, Japanese Unexamined Patent Application Publication No. 2005-534199, for example). Such a magnetic sensor using GMR elements can relatively improve detection sensitivity and responsibility and can provide stable detection property against a change of temperature. Specifically, by detecting an induction magnetic field using a Wheatstone bridge circuit that includes four GMR elements, sensitivity and accuracy can be further improved compared with the case where only one GMR element is used.